State and federal health authorities are focusing on the role of contaminants or counterfeit substances as a likely cause of vaping-related lung illnesses - now up to 354 possible cases in 29 states, nearly double the number reported to be under investigation last week, The Washington Post has learned.

The investigation is "starting to point to what solvents are being used, and that can vary a lot"- especially in counterfeit or black-market products, including potentially mislabeled solvents that consumers buy themselves to make do-it-yourself "home brews," said an official at the Centers for Disease Control and Prevention, which is heading the investigation.